Steerable antenna



y 1963 o. M. WOODWARD, JR.. ETAL 3,090,956

STEERABLE ANTENNA Filed Dec. 23, 1960 '7 Sheets-Sheet 1 N VEN TORI fin 1y 4% marl/m J? 1 JM/i Ema w fifiisarv y 1963 o. M. WOODWARD, JR., ETAL 3,090,956

STEERABLE ANTENNA Filed Dec. 25, 1960 '7' Sheets-Sheet 2 y 1963 o. M. WOODWARD, JR.. ETAL 3,090,956

STEERABLE ANTENNA Filed Dec. 25, 1960 7 Sheets-Sheet 3 lrmekr/ v May 21, 1963 Filed Dec. 23, 1960 O. M. WOODWARD, JR" ETAL STEERABLE ANTENNA vim/M635 7 Sheets-Sheet 4 y 1963 o. M. WOODWARD, JR.. ETAL 3,090,956

iffdi/viy United States Patent 3,090,956 Patented May 21, 1953 ti an 3,090,956 STEERABLE ANTENNA Oakley M. Vloodward, in, Princeton, and John Bruce Rankin, Cranhnry, N.J'., assignors to Radio Corporation of America, a corporation of Delaware Filed Dec. 23, 1960, Ser. No. 77,979 14 Ciaims. (Ci. 343-100) This invention relates to directional antennas and more particularly to improved antennas capable of propagating and/or receiving one or more radiation beams, electronically steerable in a horizontal plane and, if desired, in a vertical plane.

Many types of beam propagating antennas are known wherein scanning of the beam is controlled by mechanical movement of the antenna in horizontal and vertical directions. Electronic scanning has been proposed employing antenna structures such as broadside arrays. One such proposed structure includes several broadside arrays arranged in a geometrical figure such as a square or hexagon. Any such structure has the disadvantage that it is only possible to propagate a true desired field pattern in one specified direction with respect to a face of the polygonal structure. As a beam is scanned through an angle progressing toward 90 from normal the field pattern becomes progressively more and more distorted. Normally each broadside array includes a multiplicity of radiating elements. For scanning purposes, each radiating element is separately excited by its own generator. Thus, a further disadvantage becomes evident when one considers the number of generators and the complex circuitry required. Also disadvantageous is the fact that each array of a polygonal structure propagates only in a given sector. Thus, when a beam is scanned through such a sector, radiating elements of only one array are energized, those of other arrays being deenergizcd and contribute nothing to the formation of the beam pattern in the given sector. Reception of beam patterns with a broadside array structure entails problems corresponding to those set forth above.

It is a general object of the invention to provide an improved steerable antenna structure for propagating or receiving beam patterns which are electronically scanned.

It is a further object of this invention to provide an improved electronically scanning antenna capable of propagating a beam pattern and rotating that pattern through 360 with minimum distortion.

It is a further object of this invention to provide an improved electronically scanning antenna having a multiplicity of excited radiating elements which contribute to the formation of a beam pattern.

It is yet a further object of this invention to provide an improved electronically scanning antenna having a multiplicity of radiating elements requiring a minimum of generators for excitation of the elements.

It is still a further object of this invention to provide an improved steerable antenna capable of propagating or receiving a plurality of beams independently scanned by electronic means.

These and other objects and advantages are provided in accordance with the invention which comprises an improved steerable antenna having, for example, at least one pair of upper and lower conductive members preferably spaced apart a distance up to one-half wavelength and defining a radial waveguide having a cylindrical aperture. Within the waveguide, means are provided for exciting a mode which alone would provide omnidirectional propagation from the waveguide. Additional means are provided for exciting a plurality of modes in the waveguide which would, if excited independently, propagate separate rosette radiation patterns, each such pattern having an even number of lobes, the number of lobes in one pattern differing from the number in any other pattern. All modes are excited simultaneously to form one or more beams, rotation of which is provided for by phasing means associated with each rosette propagating means. The phasing means may be mechanically or electronically controlled in unison to provide the desired scanning of one or more transmission beams or receiving patterns.

The invention and embodiments thereof are described in greater detail in the following description and illustrated in the drawings wherein:

FIG. 1 is an elevational view of an antenna constructed in accordance with a preferred embodiment of this invention;

FIG. 2 is a cross-sectional view taken along the line 22 of FIG. 1 showing the relative locations of the radiating elements of the embodiment of FIG. 1;

FIG. 3 is an enlarged elevational view partially in cross-section, of the central portion of the embodiment of FIG. 1;

FIG. 4 is an enlarged elevational view partially in cross-section, of a portion of the embodiment of FIG. 1 near one edge thereof;

FIG. 5 is a schematic view in perspective illustrating an arrangement for feeding the radiating elements of the embodiment of FIGS. 1 to 4;

FIG. 6 is a schematic circuit diagram of an electromechanical phasing network for feeding the radiating elements of the embodiment of FIGS. 1 to 4 to produce a single radiating beam;

FIG. 7 is a cross-sectional view of a coaxial hybrid for use in the network of FIG. 6-;

FIG. 8 is a cross-sectional view of a telescoping adjustable trombone electromechanical phasing element which can be effectively employed in the network of FIG. 6;

FIG. 9 is a crosssectional view of a coaxial M4 wave transformer connected to a reactive power splitter for use in the network of FIG. 6;

FIG. 10 is a plan view of the power splitter of FIG. 9 with the top cover removed to show the interior thereof;

FIG. 11 is similar to FIG. 6 except that the network of FIG. 11 provides means for producing two independent radiating beams;

FIG. 12 is a schematic circuit diagram of an electronic circuit for feeding the radiating elements of the antenna of FIGS. 1 to 4;

FIG. 13 is a schematic circuit diagram of a generation signal mixer for use in the circuit of FIG. 12;

FIG. 14 is a schematic circuit diagram of a recovery signal demodulator for use in the circuit of FIG. 12.

Similar elements are designated by similar reference characters throughout the drawings.

A preferred embodiment of the antenna of this invention, as shown in FIG. 1, comprises a radial waveguide defined by two flat metal plates 29 and 22 spaced apart a distance of up to /2 wavelength. The edges of the two plates are preferably flared, to form a cylindrical horn 24 to provide the proper vertical beam pattern and to improve impedance matching with free space. Parallel spacing between the two metal plates 26 and 22 is maintained, for the most part, by a cylindrical support 26 of relatively thin dielectric material. The support 26 is shown as being cut away at the center to provide a view of the interior of the radial Waveguide. At the center of the radial waveguide, there is located a monopole radiating element 28 capable, upon excitation, of propagating an omnidirectional beam pattern. This central monopole 28 also functions as a conduit for coaxial transmission line 49 (FIG. 2) the function of which will be described hereinafter. A plurality of short monopoles are suspended through apertures in the top plate 20, four such 38 61a, 38e and 34g being shown in FIG.

1. An additional plurality of short monopoles, such as 33g, 37a, 31b and 37h projects upward through apertures in the bottom plate 22. The length of each of the short monopoles is preferably between A5 and A wavelength.

In the cross-sectional plan view of FIG. 2, the central monopole 28 and four concentric rings of short monopoles are illustrated. Each complete ring of monopoles comprises two sub-rings. For example, the innermost ring comprises a sub-ring of two monopoles 31a and 31b which project upward from the bottom plate 22 and another sub-ring of two monopoles 32a and 32b which depend through apertures in the top plate (FIG. I). Radially outward three more complete monopole rings, each comprising two sub-rings, are located.

In an embodiment constructed as shown in FIGS. 1 and 2 and designed to operate at a center frequency of about 765 megacycles, the antenna has an overall diameter of about four feet. The two plates 20 and 22 are spaced apart about A wavelength and the edges thereof are flared into a 60 cylindrical horn 24. The radiating elements in the sub-rings are about /5 wavelength monopoles, each sub-ring having its monopoles circumferentially spaced about /2 wavelength apart. In each complete ring one monopole of one sub-ring is equidistant (i.e. about A wavelength) from two adjacent monopoles of the other sub-ring in that complete ring. In each complete ring all monopoles are preferably of equal length. The length of the monopoles in one ring may, however, dilfer from the length of those in another ring. As shown, one long monopole 28 is located at the common center for all the concentric rings. Radially outward from the central monopole 28 is a first complete ring of monopoles (the innermost mentioned above) two of which 31a and 31b project above the bottom plate 22 (FIG. 1) and two of which 32a and 32b depend from the top plate 20 (FIG. 1). Eight monopoles make up the next complete ring, one subring comprising four monopoles 33a to 33d and the other sub-ring also comprising four monopoles 34a to 34d. The next complete ring has two sub-rings of 6 monopoles each, these being shown as 35a to 35 and 36a to 36f respectively. The final complete ring has an 8 monopole sub-ring 37a to 37h and another 8 monopole sub-ring 38a to 38k. As mentioned hereto-fore, monopoles of each sub-ring are spaced apart a circumferential distance of about /a wavelength. One monopole of one sub-ring is equidistant from two adjacent monopoles of the other sub-ring in each of the complete rings.

In the antenna as shown in FIG. 2, the central monopole 28 is excited to produce an omnidirectional radiation pattern. The innermost ring of monopoles which includes two sub-rings 31 and 32 produces a four-lobe rosette radiation pattern. In a similar manner the next ring, which includes sub-rings 33 and 34, produces an eight-lobe pattern; the ring which includes sub-rings 35 and 36 produces a twelvelobe pattern; and the outermost ring, which includes sub-rings 37 and 38, produces a sixteen lobe pattern. When energy is fed to all of the sub-rings in the proper phase, the omnidirectional and rosette patterns are combined to produce a single beam in the desired direction L=0. The phasing re quired to produce this beam and that required to steer the beam in any direction is described in detail hereinafter. Also described hereinafter is the phasing required to produce and independently steer two radiated beams.

In FIG. 3, the central monopole 28 is shown as a conducting tube in electrical contact with the upper plate 20 and connected to the inner conductor of a A wavelength stub 47 which is attached to the bottom plate 22. The outer surface of the conducting tube 28 is fed from a coaxial input 49, the center conductor 41 of which is connected to the outer surface of the conducting tube 28 at a point near the upper end of the quarter wave stub 47. Coaxial feed lines 42, for transmitting energy to the monopole sub-rings 32, 34, 36 and 325 (FIG. 1), suspended from the top plate 20, pass through the conducting tube 28. By passing the feed lines 49 through the conducting tube 28 the internal fields in the radial waveguide are undisturbed by such feed lines.

In FIGURE 4, there is shown the manner in which the monopole elements of the sub-rings are mounted. For example, a monopole 35a extending upward through the bottom plate 22 is fed from a coaxial quarter wave transformer 56). In a like manner a monopole 38a extending downward through the top plate 20 is fed from a similar coaxial quarter-wave transformer 46. Each coaxial transformer 46 and 50 is in turn fed from subring coaxial transmission lines, the center conductors thereof 44 and 48 respectively being shown. All monopoles of the sub-rings are fed in the same manner.

FIGURE 5 illustrates a feed network for one subring of monopoles, for example, the sub-ring 35 (FIGS. 2 and 4) having 6 monopoles. RF energy from a coaxial transmission line 52 is fed to a sub-ring 48 of coaxial transmission line. The sub-ring line 48 has quarter wave transformers 50a to 50 mounted thereon at halfwave intervals. The quarter wave transformers 50a to 56f couple the sub-ring line 48' to the monopoles 35a to 35f, respectively. The coaxial transmission line 52 is coupled to the sub-ring line 48 at the junction of a quarter-wave transformer, such as 50a, and the sub-ring line 48. All the other sub-rings of FIG. 2 are fed in like manner and the sub-ring lines thereof are fed at the junction therewith of transformers associated with monopoles 31a, 32a, 33a, 34a, 35a, 36a, 37a and 38a.

The electromechanical feed network of FIG. 6 is designed to supply RF energy to the radiating elements of FIG. 2 in a phase relationship such as to produce a single scanning beam. All the transmission lines illustrated in the figure are coaxial lines and the transmitter 60, transmit-receive (TR) tube 62, sum receiver 64 and difierence receiver 66 are all well known elements of a monopulse radar system, for example, and need not be described in detail. Briefly, during a transmitting mode, radio frequency energy from the transmitter 60 is applied through the TR tube 62 to a coaxial hybrid ring 68 where it is equally divided and subsequently applied to the antenna elements. In the receive mode, antenna signals are applied to the hybrid ring 68 from which the difference voltage is applied to the difference receiver 66 and the sum voltage is applied through the TR tube 62 to the sum receiver 64. The structure and operation of hybrid ring 68 will be more fully explained in connection with FIG. 7.

One half the transmitter energy from the hybrid ring 68 is fed through a first A wave transformer 70 to a first lossless power splitter 72. The other half of the energy is fed through a second wave transformer 74 to a second lossless power splitter 76. The transformers 70 and 74 will be described in greater detail in connection with FIG. 9 and the power splitters 72 and 76 in connection with FIGS. 9 and 10.

RF power from the lossless power splitter 72 is fed into five accurately cut coaxial lines 80, 82, 84, 86 and 88. Coaxial line 80 couples the power splitter 72 to subrings 37 and 38 of FIG. 2 via a coaxial hybrid ring 121. This coaxial line 80 includes a phase adjustment trombone 1311 and has a finite electrical length, exclusive of the trombone 131. In a similar manner, coaxial lines 82, 84 and 36 are accurately cut to provide the same electrical length between the power splitter 72 and sub-rings 35 and 36, 33 and 34, 31 and 32 of FIG. 2. Each of the coaxial lines 82, 84, and 86 includes two trombones which are ignored in determining line lengths. For example, coaxial line 82 includes an adjustment trombone 132 and a phasing trombone III. The lengths of both of these trombones are ignored in calculating the proper length for the coaxial line 82.

RF power is fed to the center monopole 28 of FIG. 2 from a coaxial hybrid ring 90 through a coaxial transmission line 102 which again includes two adjustable trombones 114 and 135. The hybrid ring 90 is in turn fed from both of the power splitters 72 and 76 through coaxial transmission lines 88 and 160. In this case, the transmission line 102 has the same characteristic impedance between the hybrid ring 90 and the center monopole 28 as the other transmission lines 80, 82, 84, 86, 92, 94, 96 and 98 and transmission lines 8 8 and 100 each have a characteristic impedance twice that of line 102 between each of the power splitters 72 and 76 and the hybrid ring 90. The electrical line length from each of the power splitters 72 and 76 to the center monopole 28 is made substantially equal to that of coaxial transmission line 80, trombones 114 and 135 again being ignored. From the manner in which the aforesaid coaxial lines are cut to accurate electrical lengths, it can be seen that the transmitted power level in each of the lines 80, 82, 84, 86, 92, 94, 96, 98 and 102 Will be equal and in phase.

In order to produce a scanning beam, it is necessary that the RF energy fed to each of the sub-rings of FIG. 2 have the proper changing phase relationship. In the network of FIG. 6, this phase relationship is electromechanically provided for by a set of ganged trombones 111 to 118. These trombones are mechanically ganged together as schematically illustrated by the dashed lines 119. Structural details of the trombones will be discussed in connection with FIG. 8.

The phasing trombones 111 to 118 are inserted in all but one of the coaxial transmission lines. In FIG. 6, transmission line 80 is shown as not having a phasing trombone. Thus, the phase of the RF energy in transmission line 30 remains constant and the phase of the RF energy of all the other lines is varied with respect thereto. Any transmission line other than line 80 could have been selected to operate without phase variation. The next transmission line 82 has therein an adjustable phasing trombone 111 of a length sufficient to vary the phase of the RF energy in the line 82 through an angle A which has a value of from 0 to 360. The remaining transmission lines include longer length trombones capable of changing phase therein in multiples of A. For convenience the following table sets forth the transmission lines, associated phasing trombones and the phase angle relationship provided for by the trombones.

When the phase angle A is equal to zero, RF energy is fed to the antenna sub-rings and to the central monopole, FIG. 2, in the following manner. RF power from the transmission line 102 is fed into the A wave stub of the central monopole 28 as shown in FIG. 3, RF power for sub-rings 38 and 37 is fed into a coaxial hybrid 121 from transmission lines 80 and 92 and from there to the two sub-rings in phase at the sub-ring feed points, the energy from transmission lines 80 and 92 being fed through the hybrid 121, a A wave delay line 123 to sub-ring 38 and directly to sub-ring 37. In a similar manner, energy is fed from transmission lines 82 and 94 to sub-rings 35 and 36, from lines 84 and 96 to sub-rings 33 and 34, and from lines 86 and 98 to sub-rings 31 and 32.

As mentioned heretofore monopoles 31a and 38a, FIG. 2, are located, in each sub-ring, at the feed point for that sub-ring. It isto be noted that these monopoles are not located along any common diameter of the antenna. If,

then, the line 39 is selected as azimuth angle0 for the beam radiated from the antenna, phase adjustment of the RF energy fed to each sub-ring and to the central monopole 28 will be required. The required phase delay adjustment is set forth in the following table wherein 1=wavelengthz Table 11 Phase Sub-ring Feed Point Adjustment x Central monopole 28 5 36. 36a 37a {is}! The foregoing phase adjustments could be incorporated into the transmission lines to 88, 92 to 98 and 102 of FIG. 6 by accurately cutting those lines to the proper electrical lengths. However, it is more expedient to insert adjustable trombones in the transmission lines to provide the appropriate phase adjustments. Such additional trombones can also serve the dual function of compensating for discontinuities in the transmission lines. In FIG. 6, discontinuity compensation and phase adjustment is provided for by nine individually adjustable trombones 131 to 139. Each trombone is initially set to provide the phase adjustment set forth in Table II and then further adjusted by a small increment 5 to compensate for line discontinuity. The total adjustment required is set forth in the following table:

Table III Compensa- Adjust- Transmission line ting merit Trombone 39 131 +5so 82. 132 +5s2 94 13s gain Adjustment of the compensating trombones 131 to 139 as set forth in Table III will cause the transmitted beam of the antenna to point in the direction 4=0 as shown by the radial line 39 in FIG. 2. Once a beam direction 4=0 is established, the beam can then be steered in a desired azimuthal direction. By changing the lengths of the ganged trombones 111 to 118, as shown in Table I, the beam can be steered to any desired angle is a counter-clockwise angle when A increases as a result in an increase in length L+ of the trombones 111 to 118. The angle through which the beam is steered is governed by the following expression:

27L =A+ radians A =A radians FIG. 7 shows a suitably constructed coaxial hybrid ring for use wherever a hybrid is called for in FIG. 6. The hybrid comprises a ring-shaped coaxial line 141 having four input-output coaxial arms 143, 145, 147 and 149, the central conductors 143a, 145a, 147a and 149a of which are all connected to the central conductor 141a of the ring shaped line 141. The outer conductors of the coaxial arms 143, 145, 147, and 149 are connected to the outer conductor 14111 of the ring-shaped line 141 as shown at 143b, 145b, 147b, and 14%. As designed for use in the network of FIG. 6, the spacing between the coaxial arms 143 and 145, 145 and 147, and 147 and 149 is, in each instance wave length; the spacing between coaxial arms 143 and 149 is equal to %wavelength. When used as one of the hybrids 121 of FIG. 6 for feeding the antenna sub-rings 31 to 38, RF energy is fed into the arms 143 and 147 of the hybrid; output energy is fed to the sub-rings from arms 145 and 149.

The hybrid ring of FIG. 7 may also be used as the hybrid 90 feeding the central monopole 28 as shown in FIG. 6. In this instance RF energy from transmission lines 88 and 100 of FIG. 6 is fed into the hybrid via arms 143 and 147, the output for the central monopole 28 being taken from arm 145, and the fourth arm 149 having its central conductor 149a connected through a matching resistor to ground.

A ring, such as that of FIG. 7, is also used to couple the transmitter 60 and the receivers 64 and 66 into the network of FIG. 6. When so used, the difference receiver 66 is coupled to arm 149 and the TR tube is coupled to arm 145, while arms 143 and 147 are employed to feed to and receive energy from the antenna elements.

FIG. 8 illustrates an adjustable trombone suitable for use anywhere in the network of FIG. 6 wherever such a device is called for. This trombone includes a pair of coaxial elements 151 and 153 which have the same characteristic impedance as the coaxial transmission lines, for example, transmission line 102 of FIG. 6. Coaxial element 151 corresponds to the termination in the trombone 114 of that portion of the transmission line 102 leading toward the center monopole 28. Coaxial element 153 corresponds to the termination of the portion of the transmission line 102 coming from the hybrid ring 90. The coaxial elements 151 and 153 are coupled together by a U-shaped coaxial slide 155. The slide 155 consists of an outer tube, the inner surfaces 157 and 159 of which engage the outer surface of coaxial elements 151 and 153 in sliding contact therewith, and a center tube, the inner surfaces 161 and 163 which make sliding contact with the inner conductors of the coaxial elements 151 and 153. The U-shaped slide 155 and the coaxial elements 151 and 153 are designed to have a (outward) or (inward) adjustment of sufiicient length to serve the 8 purpose for which the trombone is used in a particular transmission line. For example, in FIG. 6, compensating trombone 136 is designed with a sliding adjustment of while trombone 132 has a sliding adjustment of The shortest phasing trombone 111 is made adjustable over :360.

The A wave transformer 70 and power splitter 72 (also transformer 74 and power splitter 76) of FIG. 6 are shown coupled together in FIG. 9. Transmission line 69 couples hybrid 68 of FIG. 6 to the transformer 70. The inner conductor 171 of the transformer is constructed in three A wave steps 172, 173 and 174, the last step 174 being coupled into the power splitter 74. The stepped conductor 171 is supported within a tubular conductor 175 by, for example, insulator washers 176 and 177, made of insulating material such as Teflon.

The transformer 70 is fastened to the power splitter 74 by means of a metal flange 179 on the outer conductor 175 of the transformer. The third step 174 of the transformer inner conductor 171 is electrically coupled to a metal disc 181 in the interior of the power splitter 74. As shown in FIGS. 9 and 10, the internal disk 181 is supported between an insulating washer 182 and insulating disk 183. The washer 182 and disk 183 are in turn supported by two conductive hat-shaped plates 184 and 185. One of these plates 184 is centrally bored to accommodate the inner conductor 171 of the transformer 70, this plate 189 also having bolted thereto the flange 179 of the transformer 70. The hat-shaped plates 184 and 185 also support a ring-shaped conductive member 186.

'In the plan view of FIG. 10 the power splitter 74 is shown with the hat-shaped plate 185 and the insulating disk removed to uncover the ring-shaped member 186 and the internal conductive disk 181. Around the periphery of the member 186 are five equally-spaced coaxial connector arms 191. The center conductor 192 of each arm 191 passes through the ring shaped member 186 and is connected to the internal disk 181. Each coaxial arm 191 is adapted to have connected thereto one of the transmission lines 80, S2, 84, 86 and 88 of FIG. 6. During transmission, RF power, applied to the power splitter 74 from the transformer 70 of FIG. 9, is divided among the connector arms 191 and equally divided among transmission lines 80, 82, 84, and 86. Since transmission line 88 has twice the characteristic impedance of each of the others, it will be fed only /2 the RF power of any other line.

FIG. 11 illustrates an electromechanical phasing system for producing two independently steerable beams with the antenna of FIGS. 1 and 2. This embodiment is identical to the network of FIG. 6 except that the one set of ganged phasing trombones 111 to 118 of FIG. 6 are replaced by two sets of ganged trombones. The first such set comprises phasing trombones 201 to 204 respectively inserted into transmission lines 80, 82, 84 and 86. The second set of phasing trombones 211 to 214 are inserted into transmission lines 92, 94, 96 and 98 respectively. There is no phasing trombone in transmission line 102 for feeding the central monopole 28 of the antenna of FIGS. 1 and 2. The following table sets forth the transmission lines, associated phasing trombones and the phase angle relationship provided for by the trombones.

When a network conforming to that of FIG. 11 is used to drive the radiating elements of FIG. 2, a first beam is formed by the RF energy fed to hybrids 121 through transmission lines 80, 82, 84 and 86 and a second beam is formed by the RF energy fed to hybrids 121 through transmission lines 92, 94, 96 and 98. Since one set of ganged trombones is connected in the transmission lines 80, 82, 84 and 86, adjustment of that set will eifect steering of only one beam. In the same manner adjustment of the other set of ganged trombones 211 to 214' effects steering of the other beam.

The electronic circuit of FIG. 12 is designed to drive the radiating elements of FIG. 2 in the proper phase relationship to provide one or two electronically steered beams. For the sake of simplicity, the circuit is shown as feeding only the center monopole 28 and 4 sub-rings 31 to 34 of FIG. 2. The circuitry of FIG. 12 produces the same excitation signals to the antenna as that of FIG. 8, except that the phasing is accomplished electronically rather than by changing the length of the ganged trombones. In FIG. 12 the relative phases at the antenna terminals of the signal to be radiated (f) are controlled by a signal (f whose frequency is varied. A constant frequency (f generator 301 is connected to two identical generation signal mixers 333, 304. Also connected to the generation mixers 303, 304 are two variable or steering frequency (f,) generators 306 and 307. The outputs comprising either the upper or the lower sidebands (f if of the generation signal mixers 303 and 304 are coupled to a plurality of recovery signal modulators 311 to 316 through a pair of power splitters 72 and 76. The output (f of the steering frequency generators 306 and 307 is also fed to the recovery signal modulators 311 to 316. In the case of the recovery signal modulators 313 and 314, which are in circuit with the center monopole 28, this output (f is fed from each of the steering frequency generators 306 and 307 through two power splitters 72' and 76' which are coupled to the recovery signal modulators 313 and 314 through two equal length delay lines 317 and 318 of length L. With respect to the recovery signal modulator 312 which is in circuit with sub-rings 31 and 32, steering frequency output (i is fed through a delay line 325 to the recovery signal modulator 312. The length of this delay line 325 is made equal to L21rn radians n being an integral multiple of 277' radians at the center frequency of the steering frequency generators 306 and 307. Steering frequency output (f is also fed to recovery signal modulator 315 through a delay line 327 which has a length of L+2wn radians. The remaining recovery signal modulators 311 and 316 are fed with steering frequency output (f through associated delay lines 329 and 331, delay line 329 having a length of L-41rn radians and delay line 331 having a length of L+41rn radians. Thus the steering frequency (f applied to the recovery modulator 312 will be advanced by an angle, that applied to modulator 315 wil be delayed by an angle that applied to the modulators 311 will be advanced by an angle 2gb, and that applied to modulator 316 will be delayed by an angle 2gb.

In the recovery modulators 311, 312, 315 and 316, the phase shifted steering frequency is added to or subtracted from the sideband f if as the case may be, to provide from the recovery modulators 312 and 315 a phase-shifted output frequency f i LB and from recovery modulators 311 and 312 an output frequency 3:420. The outputs of all the recovery modulators 311 to 316 are fed through amplifiers 333 to 338, and hybrid rings 121 to the center monopole 28 and the sub-rings 31 to 34. It is to be understood that one or more additional sub-rings may be fed in the same manner with additional phase delay of the steering frequency (i i.e. i61r, -81r etc. radians.

Beam steering is accomplished by varying the steering frequency (f Each steering frequency generator can be independently varied to provide two independently steerable beams or they can be controlled simultaneously to produce a single steered beam. As the steering frequency is increased a beam will be steered in one'direction and as it is decreased the beam will be steered in the opposite direction.

With the specific example, mentioned heretofore, of an antenna designed to operate at a frequency of 765 megacycles, the frequency of the constant frequency generator 301 will also be 765 megacycles. For this purpose many commercial generators are available, one being selected which can deliver the desired amount of RF power at the operating frequency of 765 megacycles. Variable frequency generators are also commercially available for use as the steering frequency generators 306 and 307. The outputs of these generators should be fairly constant over a 273 to 334 megacycle frequency band.

The generation signal mixers 303 and 304 are preferably designed to accept inputs of 765 megacycles and 275-335 megacycles and obtain a maximum level output in the 1040 to 1100 megacycle band. Such a mixer is illustrated in FIG. 13. The constant frequency (f is fed into a diplexer 381 which may be a coaxial hybrid magic tee. In the diplexer 381 the constant frequency (i is divided into two components equal in phase and magnitude. These components are then fed through coaxial lines 382, 383, through two high pass filters 384, 385, and into two crystal cavities 386, 387, containing crystals 386' and 387 connected in series with the central conductor of the coaxial feed line. At the same time the variable or steering frequency (f,) is fed into a coaxial power splitter 388 Where it is divided into two equal components. The latter components are fed through coaxial lines 389, 390 and two low pass filters 391, 392 to the crystal cavities 386, 337. In the crystal cavities the two frequencies f and i are mixed to produce a sum frequency f -l-f This frequency f -l-f is blocked in one direction by the low pass filters 391 and 392, passes through the high pass filters 384, 385 to the diplexer 381 and thence through a high pass filter 373 which blocks the constant frequency (f The output frequency from the generation mixer of FIG. 7 is then fed to the recovery signal modulators 311 to 316 of FIG. 12.

'In the recovery signal modulators 311 to 316-, the phase-shifted steering frequency f is subtracted from the generation output frequency to provide the properly phased signal frequencies, fit), I40 and i429. A suitable mixer for this purpose is depicted in FIG. 14. The steering frequency f is fed to a crystal cavity 431 through a DC. short 403 and a low pass (340 mc.) filter 405 and at the same time the generation mixer output f -l-f is fed to the crystal cavity 431 through a high pass (1000 mc.) filter 437. In the crystal cavity these two frequencies are mixed to provide a resultant signal frequency f of the proper phase. The signal frequency is then fed through a low pass (850 mc.) filter 409 and a high pass (765 mc.) filter 411 to an amplifier (333 to 338) of FIG. 12.

In all other respects, the circuit elements of the em- 1 1 bodiment shown in FlG. l2 and the function of such elements is substantially the same as the elements and functions thereof of the embodiments of FIGS. 6 and 11.

What is claimed is:

1. In an antenna for transmitting or receiving signals at a selected operating frequency, said antenna comprising: spaced apart conductive members defining a radial Waveguide having a circular aperture, at least two means in said waveguide each propagating a rosette radiation pattern comprising an even number of lobes, the number of lobes in one of said rosette patterns being different from the number in another of said rosette patterns, and phasing means associated with at least some of said propagating means for causing rotation of said rosette patterns relative to one another.

2. An apparatus for transmitting or receiving radio energy comprising: at least one pair of conductive members spaced apart a distance up to one-half Wavelength at an operating frequency and defining a radial waveguide having a circular aperture, means within said waveguide for propagating an omnidirectional radiation pattern, means in said waveguide for propagating a plurality of rosette radiation patterns each comprising an even number of lobes, the number of lobes in one of said rosette patterns being different from the number in another of said rosette patterns, and phasing means associated with said rosette propagating means for causing rotation of each of said rosette patterns.

3. An apparatus for transmitting or receiving radio energy comprising: at least one pair of upper and lower conductive members spaced apart a distance of up to one-half wavelength at an operating frequency and defining a radial waveguide having a circular aperture, a radiating member centrally located in said waveguide for propagating an omnidirectional radiation pattern, a plurality of additional radiating members in said Waveguide for propagating a plurality of rosette radiation patterns each comprising an even number of lobes, the number of lobes in one of said rosette patterns being different from the number in another of said rosette patterns, feed means for exciting all of said radiating members to cause said patterns to combine in at least one beam emanating from said waveguide, and phasing means associated with at least one rosette pattern propagating means for controlling angular displacement of at least said one beam.

4. An apparatus for transmitting or receiving radio energy comprising: at least one pair of conductive members spaced apart a distance up to one-half wavelength at an operating frequency and defining a radial waveguide having a circular aperture, means within said waveguide for propagating an omnidirectional radiation pattern, radiating means in said waveguide for propagating a plurality of rosette radiation patterns each comprising an even number of lobes, the number of lobes in one of said rosette patterns being different from the number in another of said rosette patterns, first phasing means associated with said radiating means for causing rotation of said rosette patterns, and second phasing means sub stantially electrically decoupled from said first phasing means and associated with said radiating means for causing rotation of said rosette patterns.

5. The apparatus of claim 2 wherein said phasing means comprises a plurality of mechanically coupled phase shifters, each associated with one of said rosette propagating means.

6. An apparatus for transmitting or receiving radio energy comprising: at least one pair of conductive members spaced apart a distance up to one-half wavelength at an operating frequency and defining a radial Waveguide having a circular aperture, means within said waveguide for propagating a plurality of rosette radiation patterns each comprising an even number of lobes, the number of lobes in one of said rosette patterns being different from the number in another of said rosette patterns, means for generating said operating frequency, means for generating a variable frequency, means for combining said frequencies to produce a side band frequency, a plurality of phase shifting means coupled to said means for generating said variable frequency, each said phase shifting means producing a different phase change from that produced by another thereof, a plurality of means for combining said sideband and said phase shifted variable frequency to produce a plurality of phase shifted operating frequencies and means for feeding to each of said rosette propagating means a different one of said phase shifted operating frequencies.

7. An antenna for transmitting or receiving comprising spaced apart conductive members defining a radial waveguide having a circular aperture, at least two means in said waveguide for propagating a plurality of rosette radiation patterns each comprising an even number of lobes, the number of lobes in one of said rosette patterns being different from the number in another of said rosette patterns. 8. The antenna of claim 7 including means in said waveguide for propagating an omnidirection radiation pattern.

9. The antenna of claim 7 wherein said conductive members are spaced apart a distance of up to one-half Wavelength at an operating frequency.

10. The antenna of claim 9 wherein each said means for propagating said rosette patterns comprises an even number of radiating elements positioned about one-quarter wavelength apart about the circumference of a circle, each of said circles having a diameter different from another of said circles.

11. An antenna for transmitting or receiving comprising at least one pair of conductive members spaced apart a distance up to one-half wavelength at an operating frequency and defining a radial waveguide having a circular aperture, means within said waveguide for producing an omnidirectional radiation pattern, a first plurality of means in said Waveguide for producing a corresponding plurality of rosette patterns each comprising an even number of lobes, the number of lobes in one of said rosette patterns being different from the number in another of said rosette patterns.

12. The antenna of claim 11 wherein each of said plurality means for propagating rosette patterns comprises an even number of radiating elements positioned about onequarter wavelength apart about the circumference of a circle, each said circle having a diameter different from another of said circles, alternate radiating elements in any one circle being associated with one of said conductive members and each radiating adjacent an alternate element being associated with the other of said conductor members.

13. An antenna for transmitting or receiving comprising a pair of conductive plates spaced apart a distance of up to one-half wavelength at an operating frequency to define a radial Waveguide having a circular aperture, the outer edges of said plates being flared to form a cylindrical born; a monopole radiating element positioned in the center of said radial waveguide for propagating an omnidirectional radiation pattern; a number -N of sub-rings of monopoles concentrically disposed and projecting through each of said conductive plates in said radial waveguide, said monopoles of each sub-ring being circumferentially spaced apart a distance of about one-half wavelength; and connection means associated with each of said sub-rings of monopoles for feeding energy thereto at said operating frequency.

14. An antenna for transmitting or receiving comprising a pair of conductive plates spaced apart a distance of up to one-half wavelength at an operating frequency to define a radial waveguide having a circular aperture, the outer edges of said plates being flared to form a cylindrical born; a monopole radiating element positioned in the center of said radial waveguide for propagating an omnidirectional radiation pattern; a number N of sub-rings of monopoles concentrically disposed and projecting through each of said conductive plates in said radial waveguide, each said sub-ring including 2N monopoles 'where N in- 13 creases outwardly toward said circular aperture, said monopoles of each sub-ring being circumferentially spaced apart a distance of about one-half wavelength; at onequarter wave transformer coupled to each of said monopoles; a sub-ring transmission line coupled to all of the transformers associated with the monopoles of any one of said sub-rings and connection means on each of said 14- sub-ring transmission lines for feeding energy thereto at said operating frequency.

References Cited in the file of this patent UNITED STATES PATENTS Litchford May 4, 1954 

11. AN ANTENNA FOR TRANSMITTING OR RECEIVING COMPRISING AT LEAST ONE PAIR OF CONDUCTIVE MEMBERS SPACED APART A DISTANCE UP TO ONE-HALF WAVELENGTH AT AN OPERATING FREQUENCY AND DEFINING A RADIAL WAVEGUIDE HAVING A CIRCULAR APERTURE, MEANS WITHIN SAID WAVEGUIDE FOR PRODUCING AN OMNIDIRECTIONAL RADIATION PATTERN, A FIRST PLURALITY OF MEANS 